1. Field of the Invention
This invention relates to thin film magnetic transducers having an improved writing characteristic and more particularly to an improved thin film magnetic transducer having one or more magnetically conductive layers formed of a material having selected chemical, magnetic and physical properties which cooperates with the magnetic material forming the pole pieces to reduce pole piece saturation in response to a write current and to increase the magnetic flux density in the gap during the writing of information on adjacent magnetic media resulting in greater
2. Description of the Prior Art
Thin film magnetic transducers are known in the prior art. One such typical thin film magnetic head formed by vacuum deposition is disclosed in an article entitled "Thin-Film Magnetic Heads Excel in Packing and Moving Data" by Thomas A. Roscamp and Paul D. Frank which appeared in the Mar. 3, 1977 issue of Electronics.
The use of thin film magnetic transducers has enabled fabrication of integrated thin film magnetic heads which have improved frequency response, higher bit packing density, higher track density and increased reliability; typically, bit packing densities of 12,000 bits per inch and 1,000 tracks per inch can be achieved with integrated thin film transducers.
During the reproducing or reading operation, thin film magnetic transducers having pole pieces comprising a single layer magnetically oriented film exhibit Barkhausen noise due to the presence of magnetic domains and the resulting nonuniformity in switching. A means of overcoming domain formation by use of a plurality of separate magnetic layers with alternating magnetizations is described in the abovereferenced article by Roscamp and Frank which appeared in the Mar. 3, 1977 issue of Electronics.
In addition to thin film magnetic transducers producing Barkhausen noise during switching, such known thin film transducers produce delays and distortions of the read signals. The delays and distortions so produced are due to variable domain structures which occur in single, magnetically oriented layers which define the pole pieces. The domains in the thin film pole pieces can be observed using known Bitter pattern techniques. Delays are introduced into the read signals due to the time required for domain walls to move in response to information recorded on the magnetic media. The above effects are discussed in detail in an article entitled "Domain Effects In The Thin Film Head" by R. E. Jones, Jr., which appeared in the November 1979 IEEE Transactions on Magnetics, Volume MAG-15, No. 6.
Thin film magnetic recording heads having a high permeability magnetic material formed of an iron-nickel-chromium alloy wherein a plurality of separate magnetic layers are used to form magnetic legs in which the demagnetizing field is reduced to avoid formation of domains within each magnetic layer to improve writing and reading characteristics are disclosed in an article entitled "Integrated Magnetic Recording Heads" by Jean-Pierre Lazzari and Igor Melnick which appeared in the IEEE Transactions on Magnetics, Volume MAG-7 No. 1, March 1971.
Also, the general concept of using two spaced parallel magnetic elements, each of which has its magnetic domains oriented in opposite directions, is disclosed in French Patent No. 6936864.
The geometry of the thin film magnetic layers may be varied in length, width, thickness and interpole separation. Such elements affect the magnetic circuit reluctance and, most importantly, the maximum flux within the pole pieces before saturation. The effects of the geometrical limitations are discussed in an article entitled "Finite Element Analysis of Vertical Multi-turn Thin-film Head" by Eric R. Katz which appeared in the September 1978 IEEE Transactions on Magnetics, Volume MAG-14, No. 5.
However, the known prior art thin film transducers having single layers of oriented magnetic material have an inherent limitation in terms of pole piece saturation and domain wall movement which constrain efficiency in writing on magnetic media and result in distortion and delay in reading from such magnetic media.
Another inherent limitation imposed on known thin film transducers is the trade-off of thickness of the pole pieces versus the achievable recording density on magnetic media. A thin film transducer requires thin pole pieces to obtain high recording resolution but this limits the flux saturation levels. Conversely, a thin film transducer having thicker pole pieces has a lower recording resolution, but a higher flux saturation level. In designing the prior art thin film transducers, it was necessary to compromise between the recording resolution and flux saturation level by selectively controlling the thickness of the pole pieces.